1. Field of the Invention
The present invention relates to a method and system for reclamation and purification of a substantial part of household waste water. Particularly, a novel system and method for reusing graywater are provided, using the principles of vertical flow constructed wetlands.
2. Description of the Prior Art
As the standard of living rises, and as the world population increases, the demand for freshwater soars. The available sources of fresh water are quite limited around the world, and in many cases they are distributed unevenly in space or time. Environmental concerns and a steep increase of water prices motivate reusing as much household wastewater as possible [Rogers P.: Scientific American 299, August 2008, 28-35].
Current methods of recycling non-potable water need expensive and complex equipment to be installed and maintained, and require large amounts of energy. Cheap and technologically simple solutions to the problems of reusing household water, however, could substantially alleviate periodic or chronic water shortage in many areas, as well as affording significant saving of freshwater at both national and global levels. In recent years, graywater has become a target for saving in households. Graywater is any wastewater used in the home, except from toilets, including bathwater and the discharge following washing clothes and dishes, comprising 50-80% of the total household consumption; various attempts have been made to use graywater, instead of disposing it in sewage, for irrigating gardens or for other uses not requiring potable water.
U.S. Pat. No. 5,106,493 describes a system for processing and reusing graywater; the system comprises filtering means and chlorinating means for water purification, at least two pumps, and electromechanical control means. Additional means and modifications for manipulating graywater have since been described, including special tubing, filters, chemicals, and software. A part of wastewater can, thus, be retrieved, and more or less conveniently utilized, particularly when the house is provided with parallel graywater lines, such as described in US 2008/0175668. However, the complex and expensive plumbing installations and changes discourage many clients. Despite the importance of water saving systems, monthly savings may seem rather modest, and many people do not like to invest too much in the future, notwithstanding people in poorer areas.
A Recycled Vertical Flow Constructed Wetland (RVFCW) comprising a three-layer bed with planted organic soil overlying a filter consisting of an upper layer of tuff or plastic media and a lower layer of limestone pebbles, and a reservoir located below the bed has been disclosed. [A. Gross et al, “Recycled Vertical Flow Constructed Wetland (RVFCW)—A Novel Method to Recycle Graywater for Landscape Irrigation in Small Communities and Households”, Chemosphere 66, 2007, 916-923]
The direct flow of raw graywater into the root zone of the plant provided with the organic soil prevents bad odors and mosquitoes, and reduces the possibility of human contact and spread of disease. The graywater seeps through the porous filter towards the reservoir, further preventing development of odors and enhancing organic matter degradation and nitrification. The lime pebbles buffer the acidity produced by the nitrification and biodegradation. The water is then aerated as it falls through the air towards the reservoir. The water from the reservoir is recycled back to the upper filter, in order to dilute an additional amount of graywater and to reduce the risk of organic overload or other damage to the filter such as excess chlorination. Since water passes through the filter more than once, the required surface area in order to attain a specific water quality can be reduced. The RVFCW was found to remove virtually all the suspended solids, biological oxygen demand (BOD) and about 80% of the chemical oxygen demand (COD) after 8 hours. Although faecal coliforms dropped by 3-4 orders of magnitude from their initial concentration after 8 hours, this level was not enough to meet current regulations for unlimited irrigation.
This RVFCW is incapable of recycling graywater for extended periods of time since the filter becomes clogged with slime and sludge after a short period of time of 7-14 days. The graywater is therefore not transmitted through the filter, pooling above the planted organic soil layer, spilling outwardly from the bed without being purified. Thus this RVFCW is not suitable for providing a reliable and on-going source of recycled water for household use.
Another disadvantage associated with this RVFCW is that the graywater, as described in a similar article in Hebrew [Water and Irrigation, August, 2003, No. 442, pp. 14-21], is introduced to the planted organic soil between peat and pebble layers by means of perforated pipes. As the roots of the plant continue to grow, the perforations of the pipes become blocked with roots, thus preventing the discharge of the graywater to the filter and rendering the RVFCW useless in purifying graywater on a continuous basis.
Another disadvantage associated with this RVFCW is that the graywater is collected in a settling tank for a period of time before being introduced to the RVFCW. The graywater develops objectionable odors while remaining in the settling tank, in addition to experiencing a rapid increase in bacteria, some of which may be pathogenic. In addition, the settling tank requires periodic cleaning and disposal of the settled sludge.